Wet-strength paper and method of making same



WET-STRENGTH PAPER AND METHOD OF MAKING SAME Gerald I. Keim, West Grove,Pa., assignor to Hercules Powder Company, Wilmington, Del., acorporation of Delaware No Drawing. Application September 5, 1957 SerialNo. 682,086

Claims. (Cl. 162-164) This invention relates to the manufacture ofresintreated cellulosic fibers and fibrous products prepared therefromand is directed particularly to a method for improving the wet strengthof felted fibrous cellulosic materials such as paper, paperboard, shapedpaper articles and the like. The invention includes the improvedcellulosic fibers and fibrous products themselves as well as methods'ofpreparing these products from aqueous suspensions of fibrous cellulosicmaterial such as paper pulp.

Commercial wet-strength resins presently available do not functionefiectively at pHs much above 5.5. As a consequence, many grades ofpaper made on the alkaline side for various reasons such as'strength,softness, use.

of falkalinefillers and so on, cannot be wet-strengthened.

Moreover," the ldw pH required to effectively" use the acid-curingwet-strength resins presently available in creases machine corrosion andraises maintenance costs.

A principal object of the present invention is the pro vision of-ta".mfilhod tor adding wet-strength to -any type of paper regardless ofwhetherit is produced under acid, neutral or alkalinerconditions.

Inaaccordance with'thednvention, the-above and other objects areaccomplished'byapplying to fibrouscellulosic material such as paper pulpan uncured thermosetting In the preparation of the cationic resins:co-ntemplated for use herein, the dibasic carboxylic acid is firstreacted with the polyalkylene'polyamine, preferably in aqueoussolution,. underconditions.suchasto produce a-watersoluble polyamidecontaining-the recurring groups wh'eren and x are each 2 or more and'Ris the divalent hydrocarbon radical of the dibasic carboxylic acid.This water-solublepolyamide is then reacted with epichloro hydrin to.form the water-soluble cationic therrnosetting resin.

The dicarboxylic acids contemplated for use in preparirigthe resins. ofthe invention .are the saturated aliphatic dibasic carboxylicacidscontaining from 3'to 10carbon atoms such as succinic, adipic,azelaic and the like. The saturated dibasicacids having from 4'to8carbon atoms inthe molecule are preferred." Blends of two or. more ofthe saturated 'dibasic carboxylic acids may;.also.

be used."

A variety of polyaltkylene polyamines including polyethylene polyamines,polypropylene polyamines, polybutYlenepo1yamines-and so "on may beemployed of which It hasbeen found that resins of,

nited States Patent- 6 Z,926, l l6 Patented Feb. 23, 1960 thepolyethylene polyamines represent an economically;

preferred class. More specifically, the polyalkylene polyaminescontemplated for use may be represented as polyamines in which thenitrogen atoms are linked together by groups of the formula -C,,H wheren is a small integer greater than unity and the number of such groups inthemolecule ranges from two up to about eight. nitrogen atoms may beattached to adjacent carbon atoms in' 'the group -C,',H or to carbonatoms further apart, but not to the same carbon atom. This inventioncontemplates not only the use of such. polyamines as diethylenetriamine,triethylenetetramine, tetraethylenep enta mine, and dipropylenetriamine,which can be obtained in' reasonably pure form, but also mixtures and.various crude polyamine materials. of polyethylenepolyamines obtained bythe reaction of ammonia andethylene dichloride, refined only to theextent-of removal .of chlorides, water, excess ammonia, andethylenediamine, is a very satisfactory starting material. Thetennpolyalkylene polyamine employed in the claims, therefore, refers toand includes any of the polyalkylene polyamines referred to above or toa mixture of such polyalkylene polyamines.

It is desirable, in some cases, to increase the spacing of "secondaryamino groups on the polyamide moleculeenediamine, h'examethylenediamineand the like for a portion ofth polyalkylene polyamine. For thispurpose,-

up to about of the polyalkylene polyamine may be replaced by 'amolecularly equivalent amount of the diamine. will serve the purpose.

The temperatures employed for carrying out the reac tionbetween-the-dibasic-acid and the polyalkylene polyamine mayvary. fromabout C. to about 250 C. or-higher at atmospheric pressure.

reduced pressures are-employed, somewhat lower temperaturesmay-be'utiliz'ed. The time of reaction depends on'the temperatures andpressures utilized and will ordi'rlarily vary from about /2 to 2 hours,although shorter or 'longer reaction times may be utilized depending onreaction conditions. In any event, the reaction is desirably continuedto substantial completion for best results.

In carrying-out the reaction, it is preferred to use anamount ofdibasicacid sufficie'nt to react substantially completelywith the primary-aminegroups of the polyalltyle'ne polyamine but insufiicient to react withthe sec-- ondary amine groups to any substantial extent. Thiswill.usually require a mole ratio of polyalkylene polyamine to dibasicacid of from about 0.921 to about 1.2: 1.

However, mole ratios of from about 0.8:1 to about 1.4:1

may be used with quite satisfactory results. Mole ratios outsideof theseranges are generally unsatisfactory.

Thus; mole ratios below about 0.8:l result in a gelled product or onehaving a pronounced tendency to gel while mole ratios above 1.4:1 resultin low molecular weight polyamides. Suchproducts do not produceefiicient wetstrength resins when reacted with epichlorohydrin.

In converting the polyamide, formed as above described," to :a-catio-nic thermosetting resin, it is reacted with. epichlorohydrin at atemperature from about 45 C. to about 100 C. and preferably betweenabout 45 C. and 70''C. until'th'e viscosity of a 20% solids solution at25 C. has reached about .Cv or higher on the Gardner- Holdt scale. Thisreaction is preferably carried out in aqueous' solution to moderateth'ereaction. pHadjustm'ent is usual ly notnecessary However, since the pHz;decreasesduringahe polymerization: phase of the reaction The Forexample, the mixture Usually; a replacement of about 50% or less' Formost purposes; however,- temperatures-between about C. and 210"C(h'avebeen found satisfactory and are preferred. Where itmay bedesirable, in some cases, to add alkali to combine with at least some ofthe acid formed. This will create an environment favoring the conversionof the chlorohydrin groups to epoxide groups, thereby increasing theratio of the latter to the former.

When the desired viscosity is reached, sufiicient water is then added toadjust'the solids content of the resin solution to the desired amount,i.e., about 10% more or less, the product cooled to about 25 C. and thenstabilized by adding suificient acid to reduce the pH at least to about6 and preferably to about 5. Any suitable acid such as hydrochloric,sulfuric, nitric, formic, phosphoric and acetic acid may be used tostabilize the product. However, hydrochloric acid is preferred.

In the polyamide-epichlorohydrin reaction, it is preferred to usesufficient epichlorohydrin to convert all secondary amine groups totertiary amine groups. However, more or less may be added to moderate orincrease reaction rates. In general, satisfactory results may beobtained utilizing from about 0.5 me] to about 1.8 moles ofepichlorohydrin for each secondary amine group of the polyamide. It ispreferred to utilize from about 1.0 mole to about 1.5 moles for eachsecondary amine group of the polyarnide.

The cationic polyamide-epichlorohydrin resins, prepared as hereindescribed, may be applied to paper or other felted cellulosic productsby tub application or by spraying, if desired. Thus, for example,preformed and partially or completely dried paper may be impregnated byimmersion in, or spraying with, an aqueous solution of the resinfollowing which the paper may be heated for about 0.5 to 30 minutes attemperatures of 90 C. to 100 C. or higher to dry same and cure the resinto a water-insoluble condition. The resulting paper has greatlyincreased wet strength, and, therefore, this method is well suited forthe impregnation of paper towels, absorbent tissue and the like as wellas heavier stocks such as wrapping paper, bag paper and the like toimpart wet strength characteristics thereto.

The preferred method of incorporating these resins in paper, however, isby internal addition prior to sheet formation whereby advantage is takenof the substantivity of the resins for hydrated cellulosic fibers. Inpracticing this method, an aqueous solution of the resin in its uncuredand hydrophilic state is added to an aqueous suspension of paper stockin the beater, stock chest,

Jordan engine, fan pump, head box or at any other'suitable point aheadof sheet formation. The sheet is then formed and dried in the usualmanner, thereby curing the resin to its polymerized and water-insolublecondition and imparting wet strength to the paper.

The cationic thermosetting resins herein disclosed impart wet strengthto paper when present therein in amounts of about 0.1-% or more based onthe dry weight of the paper. The quantity of resin to be added to theaqueous stock suspension will depend on the degree of wet strengthdesired in the finished product and on the amount of resin retained bythe paper fibers.

The uncured cationic thermosetting resins of the invention, incorporatedin paper in any suitable manner, as described above, may be cured underacid, neutral or alkaline conditions, i.e., at pHs from about 4.0 to 10,by subjecting the paper to a heat-treatment for about 0.5 to 30 minutesat a temperature from about 90 to 100 C. Optimum results, however, areobtained under alkaline conditions. In view of this, and the ratherextensive corrosion of equipment encountered at pHs below about 6.0, itis preferred to carry out the curing step at a pH from about 6.0 toabout 9.0.

The following examples will illustrate theinvention.

EXAMPLE 1 Two hundred twenty-five grams (2.18 moles) ofdiethylenetriamine and 100 grams of water were placed in a 3fneckedflask equipped with a mechanical stirrer, thermometer and condenser. Tothis was added 290 grams (2.0 moles) of adipic acid. After the acid haddissolved in the amine, the solution was heated to 185200 C. and heldthere for 1 /2 hours. Then vacuum from a water pump was applied to theflask during the period required for the contents of the flask to coolto 140 C. following which 430 grams of H 0 was added. The

polyamide solution contained 52.3% solids and had an acid number of 2.1.

To 60 grams of this polyamide solution in a roundbottom flask were added225 grams of H 0. This solution was heated to 50 C. and 12.5 grams ofepichlorohydrin were added dropwise over a period of 11 minutes. Thecontents of the flask was then heated to 60- 70 C. until it had attaineda Gardner viscosity of E. Then 150 grams of H 0 were added to theproduct, and it was cooled to 25 C. Eleven mls. of 3.7% HCl were thenadded to adjust the pH to 5.0. The product contained 9.0% solids and hada Gardner viscosity of C-D.

Tacoma-bleached kraft was beaten to a Schopper- Riegler freeness of 750cc. in a Noble and Wood cycle beater. The pulp was then adjusted to pH9.0 with V 10% NaOH and 1.0%, based on the dry weight of pulp, of thepolyamide-epichlorohydrin resin, prepared as described, was added. Thepulp was sheeted on a. Noble and Wood handsheet machine using a closedsystem in which the white water contained p.p.m. sulfate ion and hadbeen adjusted to pH 9.0 with 10% NaOH. A portion of the resultinghandsheets were given an additional cure of 1 hour at C. The sheets werethen soaked in distilled water for 2 hours and tested for wet strength.Results are listed in the table which follows Example 4.

EXAMPLE 2 A polyamide was prepared from 319 grams (2.18 moles) oftriethylenetetramine and 290 grams (2.0 moles) of adipic acid accordingto the procedure described in Example 1. The polyamide solution had a pHof 10.8, an acid number of 3.2 and contained 4.98% solids.

Sixty-three grams of the polyamide solution was dissolved in 225 gramsof H 0. This solution was stirred mechanically and heated to 50 C.Twenty-five grams of epichlorohydrin were added dropwise over a periodof three minutes. The solution was then heated to 60- 70 C. until itreached a viscosity of E (Gardner). Then it was diluted with 225 gramsof H 0, cooled to 25 C. and adjusted to pH 5.0 with 11 ml. of 3.7% HCl.The product containing 8.4% solids and having a. Gardner viscosity of C,was evaluated in bleached kraft pulp according to the procedurepresented in Example 1. Results are listed in the table followingExample 4.

EXAMPLE 3 A polyamide was prepared according to the procedure given inExample 1 using 225 grams (2.18 moles) of diethylenetriamine and 218grams (1.5 moles) of adipic acid and 94 grams (0.5 mole) of azelaicacid. Fiftyseven and one-half grams of the polyamide solution (55%solids) were dissolved in grams of H 0 and heated to 50 C. To this wereadded 15 grams of epichlorohydrin over a period of 6 minutes. Thissolution was then heated at 6070 C. until the viscosity of thecondensate reached E (Gardner). Then grams of H 0 were added and theproduct was cooled to 25 C. It was adjusted to pH 5.0 by adding 10 ml.of 3.7% HCl. The finished resin had a viscosity of B (Gardner) andcontained 9.5% solids. It was evaluated in paper according to theprocedure outlined in Example 1. Results are listed in the tablefollowing Example 4.

EXAMPLE 4 ..Sheets, of paper were prepared and tested for wet stre gth;tr mmers tiexceptrhttrnd resin was as: pdiat'ed." Theresult'sf*areset=forthiri the following table;

The following additional exammewin "further" illus'-" trate theinvention where a portion .of the polyalkylene polyamine titilizetl'ifpreparing the resinisreplaced by adiamine. Y

EXAMPLE-5' A polyamide was-prepared lfrom' therfollowing ingrei ntsDiethylenetriaminena 204.4 grams (1.9 8rno1es). Ethylenediamine....-14.0. grams (0.24 mol) Adipic acid 290Z0g'rarns (1.98 moles).

--.-.'1'00.0 grams. I

, The procedure of Example 1 was followed 'withthe (1) The reactionmixture was following exceptions. held between 180 C. and 195 C. for 45minutes; (2) aspirator vacuum was used during this entire period; and(3) the mixture was cooled to 140 C. and diluted with 43 0 ml. ofdistilled water (80 0.). amide solution contained 52.4% total solids andhad an acid number of 3.4.

To 60.5 grams of this polyamide solution were added 225.0 grams of H 0.This solution was heated to 50 The poly- C. and 11.25 grams ofepichlorohydrin was added dropwise over a period of about 11 minutes.The solution was then heated to 7080 C. and held at this temperatureuntil it had attained a viscosity of E Gardner-'Holdt. It was thendiluted with 173 ml. of water and adjusted to pH 5.0 with dilute HCl.The product contained 8.9% solids and had a Gardner viscosity of B-C.

Tacoma bleached kraft waterleaf sheets were tubsized (BO-second dip) ina 2.0% aqueous solution of the resin, prepared as above described, andadjusted to pH 9.0 with 10% sodium hydroxide. The sheets were squeezed(roll) and drum dried. Half were cured at 105 C. for one hour and thecured and uncured sheets then soaked in distilled water for 2 hours andtested for Mullen burst. The Mullen burst (pounds per square inchaverageof .five determinations) was 10.8 for the ,uncured sheets and 15.2 forthe cured sheets as compared with a Mullen burst of less than 1 forsheets which had not been treated with the resin.

It will thus be seen that the present invention makes it possible toprepare wet-strength paper under acid, neutral or alkaline conditionsand by internal addition or by surface application. While preferredembodiments of the invention have been exemplified and described herein,the invention is not to be construed as limited thereby except-as thesame may be included in the following claims.

What I claim and desire to protect by Letters Patent is: i

1. A process for the production of wet-strength paper.

cell'ul'os'ic paper stock a Water-solublecationic thermosettingresinfo'rmed by"r'eactingepichlorohydrin with' a polyamide of 516 -0saturated aliphatic' dibasic carbo'x'ylic acid and from about 0.8 'toabout 1.4 moles,

per l-hole; or dibasic acid of a polyalkylene polyamine. at atemperaturefrom about -45' C'. to about 100 C.,. said'polyaniide"acoiitaining secondary amine groups, the.

ratio of epichlorohydrin to secondary amine groups of said polya'mi'clebein'g fromabout10.5 to 1 to about 1.8'

to=-1-, adsorbingfrom about. 0.1-5% of said resin on' saidpaper stock,formingthe stocks'o treated into a sheet,- and heating th'e sheet tocure the resin toa-water-insolw 3'5 pro'e'ess for the production ofwet-strength paper which comprises addin'g to an aqueous suspension ofcellulosic paper stock a water-soluble cationic thermosett-iiig resin"formed by reacting, at a temperature from abo'ut45 C. to"about"100C.,epichlorohydrin witha polyamide of'a "Ci .satu'r'ated -aliphatic dibasiccar.- box'ylic acidp fro about-018 to'about' 1.4 moles, per

aliphatic diamine, the amount'of said aliphatic diamine not exceeding50% by weight of the polyalkylene polyamine, said polyamide containingsecondary amine groups, the ratio of epichlorohydrin to secondary aminegroups of said polyamide being from about 0.5 to 1 to about 1.8 to 1,adsorbing from about 0.15% of said resin on said paper stock, formingthe stock so treated into a sheet, and heating the'sheet to cure theresin to a water-insoluble state.

4. A process for the production of wet-strength paper which comprisesincorporating therein from about 0.1% to about 5%, based on the dryweight of the paper, of a cationic thermosettingpolyamide-epichlorohydrin resin obtained by (1) reacting a C -Csaturated aliphatic dibasic carboxylic acid with from about 0.8 to about1.4 moles, per mole of dibasic carboxylic acid, of a polyalkylenepolyamine at a temperature from about 110 C. to about 250 C. to form apolyamide containing secondary amine groups and (2) reacting thepolyamide with epichlorohydrin at a temperature from about 45 C. toabout 100 C. and at a ratio of epichlorohydrin to secondary amine groupsof the polyamide of from about 0.5 to 1 to 1.8 to l to form awatersoluble cationic thermosetting resin, said resin having been curedto a water-insoluble state.

5. A process for the production of wet-strength paper which comprisesincorporating therein from about 0.1% to about 5%, based on the dryWeight of the paper, of a cationic thermosettingpolyamide-epichlorohydrin resin obtained by (1) reacting a C -Csaturated alyphatic dibasic carboxylic acid with a polyalkylenepolyamine in a mole ratio of polyalkylene polyamine to dibasic acid offrom about 0.8 to 1 to about 1.4 to 1 and at a temperature from about160 C. to about 210 C. to form a polyamide containing secondary aminegroups, and (2) reacting the polyamide with epichlorohydrin at atemperature from about 45 C. to about 70 C. and in a ratio ofepichlorohydrin to secondary amine groups of said polyamide of fromabout 0.5 mi to about 1.8 to 1, and then curing the resin to awater-insoluble state. 6. A paper product having improved wet strengthcomprising sheeted cellulosic fibers containing from about 0.1% to 5%,based on its dry weight, of a cationic thermosetting resin, said resincomprising a watersoluble reaction product of epichlorohydrin and apoly. amide containing secondary amine groups, the ratio ofepichlorohydrin to secondary amine groups of said poly- C =G saturatedaliphatic dibasic carboxylic acid and? a polya1kyle'i1e polyamiiie in amo'le ratio ofpolyalkylene 5 polyamine -to dibasic-acid oi from about0.8 .tor1 tov about 1.4" to lt and then-curing the resin=to a water-ins.soluble'-s'tat'e'.'-* i I 29A process tor the-production of wetstrengthpaper 1 which comprises adding to an aqueous suspension ofpolyamide being obtained by heating'together ,at a temperature fromabout 110 C. to about 250. C. a C -C I saturated aliphatic dibasiccarboxylic acid and fro1nabout 0.8 to about 1.4 moles, per mole ofdibasic acid, of a polyalkylene polyamine, saidresin having been curedto a water-insoluble state. 1 g

7. A paper product having improved wet strength comprising sheetedcellulosic fibers containing -from about 0.1% to 5%, based on its dryweight, of a cationic thermosetting polyamide-ep'ichlorohydrin resin"obtained by (1) reacting a C -C saturated aliphatic dibasic carboxylicacid with from about 0.8 to about 1.4 moles, per mole of dibasic acid,of a polyalkylene polyamine at a temperature. from about 110 C.t about250 C. to form a polyamide containingsecondary amine groups and (2)reacting the polyamide with epichlorohydrin at a temperature from about,45" C. to about 100 C. and at a ratio of epichlorohydrin to secondaryamine groups of the polyamide of from about 0.5 to 1 to 1.8 to 1 to forma water-soluble pationic thermosetting resin, said resin having beencured to a water-insoluble state. I

8. A paper product having improved wet strength comprising sheetedcellulosic fibers containing .from about 0.1% to 5%, based on its dryweight, of a cationic thermosetting polyamide-epichlorohydrin resinobtained by (1) reacting a 0 -0 saturated aliphatic dibasic carboxylicacid with a polyalkylene polyamineina mole ra tion of polyalkylenepolyamine to dibasic acid of from about 0.8 to 1 to about 1.4 to l andat a temperature from about 160 C. to about 210 C. to form a polyamidecontaining secondary amine groups, and (2) reacting the polyamide withepichlorohydrin at a temperature from about C. to about C. and in aratio of epichlorohydrin to secondary amine groups of said polyamide offrom about 0,5 to 1 to about 1.8 to 1,

9. A process in accordance with claim 5 in which the dibasic carboxylicacid is a C -C saturated aliphatic I dibasic carboxylic acid. a

10. A paper product in accordance with claim 8 in which the dibasiccarboxylic acid is a C -C saturated aliphatic dibasiccarboxylic acid.

References Cited in the file of this patent UNITED STATES PATENTS2,595,935 Daniel et a1. May 6, 1952 FOREIGN-PATENTS 529,729 Canada Aug28, 1956 610,311 Great Britain Oct. 14,1948

' r OTHER REFERENCES 1 Serial No. 323,512, Hagedorn (A.P.C.),.published- April 20, 1943.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No2,926,116 February 23 1960 Gerald I. Keim It is herebfi certified thaterror appears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2 line 3O for "th" read the ---5 column 8 lines 1 and 2 forration read ratio Signed and sealed this. 23rd day of August- 1960(SEAL) Attest: v KARL H; AXLINE ROBERT C. WATSON Attesting OfficerCommissioner of Patents

1. A PROCESS FOR THE PRODUCTION OF WET-STRENGTH PAPER WHICH COMPRISESINCORPORATING THEREIN FROM ABOUT 0.1% TO ABOUT 5%, BASED ON THE WEIGHTOF THE PAPER, OF A CATIONIC THERMOSETTING RESIN, SAID RESIN COMPRISING AWATER-SOLUBLE REACTION PRODUCT OF EPICHLOROHYDRIN AND A POLAMIDECONTAINING SECONDARY AMINE GROUPS, THE RATIO OF EPICHLOROHYDRIN TOSECONDARY AMINE GROUPS OF SAID POLYAMIDE BEING FROM ABOUT 0.5 TO 1 TOABOUT 1.8 TO 1, SAID POLYAMIDE BEING OBTAINED BY HEATING TOGETHER AT ATEMPERATURE FROM ABOUT 110* C. TO ABOUT 250* C. A C3-C10 SATURATEDALIPHATIC DIBASIC CARBOXYLIC ACID AND A POLYALKYLENE POLYAMINE IN A MOLERATIO OF POLYALKYLENE POLYAMINE TO DIBASIC ACID OF FROM ABOUT 0.8 TO 1TO ABOUT 1.5 TO 1, AND THEN CURING THE RESIN TO A WATER IN SOLUBLESTATE.